PTSD can occur among civilians but is nearly twice as widespread in the military.

Previous research had shown that veterans' "fight or flight" response is overactive. In this study, researchers measured this response directly in an attempt to learn why.

The research involved 14 post-9/11 veterans who were diagnosed with PSTD and 14 without it.

Both groups were exposed to two types of mental stress, including first-person war images and sounds shown through virtual reality goggles. As this happened, their blood pressure and heart activity were monitored. Using electrodes, the researchers also recorded activity in their nervous system.

The study results revealed that the vets with PTSD had higher adrenaline levels and less control of their heart rate in response to blood pressure changes.

The findings were published May 14 in the Journal of Physiology.

"To protect patients against high blood pressure and heart disease, we need to first understand how their physiology malfunctions. We can then identify potential treatments," study leader Dr. Jeanie Park said in a journal news release. Park is an assistant professor of medicine at Emory University School of Medicine in Atlanta.

The researchers noted that their study involved veterans with PTSD specifically related to combat, and may not apply to other people with the condition.

More information

The U.S. National Institute of Mental Health provides more information on PTSD.